The present invention relates to the field of variable displacement hydraulic units, such as hydrostatic pumps and motors. More particularly, this invention relates to an extended male slipper servo pad pivotally mounted to the swashplate of such units so as to provide sliding surface area contact with the positioning mechanism. The invention results in a unique swashplate assembly that has few parts and is economical to produce.
Various arrangements are known for connecting the swashplate of a variable displacement hydraulic unit, such as a pump or motor, to a positioning means or mechanism such as a servo piston or a bias piston. In one such arrangement a cammed button is press fitted into the swashplate. This provides a sliding line contact on the servo piston or bias piston. A second arrangement involves a domed servo piston or bias piston running against the swashplate. This provides a sliding point contact. Pin and link connections have also been tried. Another known arrangement involves attaching a female slipper to a male piston in a crimping or swedging operation. The male piston end of this piston-slipper assembly is then pressed into a cylindrical hole in the swashplate. With this arrangement, multiple operations are required to provide a swashplate assembly that is ready for connection with the positioning mechanism. Therefore, there is a need for an improved connection of the swashplate to the positioning mechanism in a variable displacement hydraulic unit.
A primary objective of the present invention is the provision of an improved connection between the swashplate and swashplate positioning mechanism of a variable displacement hydraulic unit.
Another objective of the present invention is the provision of an extended male slipper having a ball end pivotally attached to the swashplate and a pad end adapted to provide surface area contact with the positioning mechanism.
A further objective of the present invention is the provision of a connection between the swashplate and the swashplate positioning mechanism that is economical to produce and reliable in use.
These and other objectives will be apparent from the drawings, as well as from the description and claims that follow.
The present invention relates to an extended male slipper servo pad pivotally mounted to the swashplate of variable displacement hydraulic units so as to provide sliding surface area contact with the swashplate positioning mechanism. The extended male slipper servo pad is pivotally secured in a socket formed in the swashplate. The slipper servo pad has a substantially spherical ball end with a major diameter disposed in the socket, an elongated neck portion, and a pad end having a substantially flat planar surface thereon directed away from the ball end. The substantially flat planar surface of the pad end provides surface area contact with a mating planar surface on the swashplate positioning means, which can include a servo piston and/or a biased piston.
In the first embodiment of the invention, the swashplate socket has a reduced diameter portion adjacent the entrance of the socket and an enlarged diameter portion adjacent to the reduced diameter portion so as to form a shoulder therebetween for retaining the ball end of the slipper servo pad, which can be press fitted into the socket. In another embodiment, a sleeve or bushing having a malleable ramped skirt portion is interposed between the ball end of the male slipper servo pad and the socket during installation. The ramped skirt portion, which has an outer diameter slightly greater than the diameter of the socket, bends or deforms inwardly to automatically crimp the sleeve on the ball end of the slipper servo pad and retain the same in the socket. Both embodiments provide quick and easy ways to connect the swashplate with a piston member of a positioning mechanism.